How can I help my friend who's in trouble?

Ok this is going to be long but… Ok you’ll see in my “asked ?ions” about me and my best friend and everything well this is the same friend. He lives in Hamilton and I live in St. Catharines (1/2 hour apart) and well he told me hes hanging out with these “partiers” and I told him “he can make his own desicions, and im not against drinking and drugs, but I’ve seen it 1st hand of it all going wrong (my dad WAS a alcoholic. pot addict, and crack addict)” the about a couple of weeks later he come on msn, he doesn’t have internet so I asked him if he was at a friends and well it was one of his “partier” friends Brittany well she calls me a hoe, slut, and that I suck and she rocks and that he doesn’t care about me and that shes he best friend, and I told her that he can be friends with who ever he wants to, and 1 month (theve been friend for about 1 month) can’t compare to our 9 years. Well he came on msn a few days later at another, good friends house, I told him and sent him the convo and he said nothing was true and that hes never lied to me, and that this brittany girl was not like this in person but he didn’t seem upset or angry about what this new girl said to his best friend. Well not only that hes hanging around these people that worries me is that hes had a hard life and he could easily get hooked and him and his family moved but they still have 2 weeks on there old place so he is staying there by himself with these people around him and his phone is disconnected so I can’t get a hold of him. hes already cancelled our plans, and well he went to his new house and left a message on my machine because I wasn’t home and sounded really sad and troubled and I havn’t been able to get a hold of him and im worried what should I do and what should I say. I’ve told him I don’t like this girls and I have a really bad feeling about them all, and that I trust him but I dobn’t trust these new “friends of his” HELP ME PLEASE